1. Field of the Invention
The present invention pertains generally to the field of radar signal processing and more particularly to the processing of radar signals for detection of an object where at least one of the radar or object are moving.
2. Background of the Invention
Radar systems, including ultra wideband (UWB) radar systems are often employed to detect moving objects. The moving objects of interest vary from system to system and may include objects as diverse as an aircraft, a weather system, a person, a golf ball, a bird, a car, or other objects, as may be of interest. Ultra wideband is particularly advantageous for short range detection because of the fine range resolution available due to the ultra-wide bandwidth. Various approaches to UWB radar have been described in the literature that utilize signal architectures including pulse trains, coded pulse trains, and wide band code modulated RF. All of these systems can achieve a very narrow range resolution bin by virtue of their extremely wide bandwidth.
When UWB radar is used for detecting stationary objects, the sensitivity of the radar can theoretically be increased without limit simply by integrating the return signal indefinitely. In practice, however, there are limitations in the stability of the electronics and in the time allowed to achieve a result that prevent unlimited integration.
For moving objects, the motion of the object presents a further limit on the possible integration time for object detection. Motion affects both the instantaneous phase of the response as well as the amplitude. If the object moves more than ¼ wavelength of the center frequency of the UWB signal during the integration time, the structure of the object signature may be significantly affected. If the object moves more than the range equivalent of the resolution bandwidth or more than the length of the object during the integration time, the object may move entirely out of the response bin, resulting in integration of noise alone, without an object response signal, reducing rather than increasing system sensitivity.
Conventional techniques for detecting moving objects include subtracting previous scan information from the current scan to look for differences resulting from the position shift of the object due to object motion over time. This technique can improve object detection in stationary clutter, but does not improve the object signal to noise ratio without clutter and is of limited utility against moving clutter. Thus, there is a need for improved techniques for detection of moving objects using ultra wideband radar that can increase the signal to noise ratio of the object response and that are effective against moving clutter.
Radar systems, including UWB radar systems are often employed on moving platforms to detect stationary objects. For example, UWB radar has been employed on a moving projectile to act as a proximity fuze to cause detonation of a projectile at a desired distance from a stationary target as described in U.S. patent application Ser. No. 10/971,427, filed Oct. 22, 2004. U.S. Patent Application No. 60/651,016, filed Feb. 8, 2005; and U.S. Patent Application No. 60/671,734, filed Apr. 15, 2005; all of which are incorporated herein by reference. However, because it is not feasible to sharpen the beam significantly by modifying the electromagnetics of the antenna system because of its small size, there is a need for improved techniques for the removal of clutter in radar return signals transmitted and received by a radar on a moving platform.